This invention relates generally to a metal deposition cell and more particularly to a brushless electroforming apparatus employing a conductive liquid contact. The apparatus and processes described herein are illustrated primarily in the context of an electroforming process, but such apparatus and processes may be useful for other metal deposition processes including electroplating. The resulting electroformed articles are used for example as substrates in the fabrication of photoreceptors.
Electroforming apparatus often employ solid metal brushes and slip rings to provide current continuity between the current source and the mandrel. However, solid metal brushes are problematic: they eventually wear out which necessitates replacement; they may spark, and they may skip on the slip ring which would cause the voltage to fluctuate. This skipping and sparking also cause the slip ring to become pitted and bumpy (like what happens when a welding rod is touched against an electrically hot surface). The resulting pitting and bumpiness become a spot where a spark is generated each time a brush passes over it. Eventually the slip ring must be refinished (machined and often replated with silver). Another problem is that the brushes also pit which accelerates their wear and reduces their contact area which increases the contact voltage. If the contact voltage gets too high, the brush may burn causing instantaneous catastrophic failure. Indeed, the entire drive may be destroyed as well as the electrolyte. Note that solid nonslip systems also may exist where there is solid to solid contact. In addition, the mandrel is typically rotated during the electroforming process to nullify anode to cathode alignment perturbations and/or to obtain sufficient agitation to make it possible to deposit metal at an economical rate. However, conventional electroforming apparatus combine the mandrel rotation function with the current continuity function which increases the complexity of these systems, thereby causing a disproportionate amount of maintenance expense. Thus, there is a need for a brushless electroforming apparatus which minimizes wear, sparking skipping, and voltage fluctuations. There is also a need for a brushless electroforming apparatus which separates the mandrel rotation function and the current continuity function to minimize maintenance expense.
Various electroforming apparatus and processes are known: Bailey et al., U.S. Pat. No. 3,844,906 and Wallin et al., U.S. Pat. No. 3,876,510.